1. Field of the Invention
This invention relates to an information signal reproducing apparatus and more particularly to an apparatus for reproducing an information signal by periodically tracing, with a reproducing head, a recording medium on which pilot signals of n kinds (n: an integer which is at least 3) having different frequencies are recorded along with the information signal, in a cycle of n tracks, in many tracks formed in parallel with each other.
2. Description of the Related Art
Some of so-called rotary two-head helical scanning type video tape recorders (VTRs) of the above stated kind are arranged to perform tracking control in accordance with a so-called four-frequency method. In the following description of this specification, the VTR of this kind will be described by way of example.
The four-frequency method for tracking control enables the VTR to detect a tracking error without recourse to the use of a fixed head. The method is advantageous also in that a tracking error signal which is thus obtained shows an actual relation between the information signal and the recording tracks. Therefore, the four-frequency tracking control method is considered highly suited for rotary-head type recording/reproducing apparatuses typically represented by the VTR.
Meanwhile, the VTR is generally arranged to be capable of setting any of at least two different track pitches in recording. In cases where recording and reproduction with a high picture quality are desired by the operator, recording and reproduction are performed in a so-called standard mode (hereinafter referred to as the SP mode) which gives a wide track pitch. In case that continuous recording over a long period of time on a single coil of tape is required, recording and reproduction are performed in a so-called long-time mode (hereinafter referred to as the LP mode) which gives a narrow track pitch.
With the VTR thus arranged to be capable of setting any of a plurality of track pitches, it is necessary in performing reproduction to automatically detect the recording track pitch and to adjust the tape transport speed, etc., to the recording track pitch detected.
For the VTR of the kind performing the four-frequency type tracking control, various methods have been proposed and put into practice for discriminating the track pitch of the recording medium by utilizing the pilot signals reproduced. For example, U.S. Pat. Nos. 4,691,256 and 4,714,970 etc. have disclosed such methods. In discriminating the track pitch with the VTR of the kind performing the four-frequency type tracking control, however, the discriminating action might become inaccurate as it is apt to be affected by inadequate linearity of the tracks, the drop-out of a reproduced signal, etc. Therefore, for increased reliability, discrimination signals must be statistically processed. However, this necessitates an excessively long period of time for the discriminating action.
Besides, in the apparatus of this kind, the state of tracking control is not easily surmisable. An attempt to enable the apparatus to make the above stated discrimination within a short period of time, therefore, tends to increase the possibility of erroneous detection.
Further, unevenness in the degree of mechanical precision between one unit of the apparatus and another causes some delicate differences in the tracing state of the head among different units. This has caused either an erroneous discrimination or inability to discriminate.
It has been another problem that, in the event of a reproducing operation on a recording medium, or tape, which has its track pitch change from one pitch to another at some intermediate point thereof, a signal reproduced deteriorates over a long period of time, because: It is extremely difficult, in connection with the above stated variable factors, to analyze how the tape is moved under the tracking control during the track pitch discriminating action.
In the VTR performing the four-frequency type tracking control, the level of a tracking error signal becomes low when the extent of a tracking error is close to the distance of two track pitches. Under such a condition, it becomes difficult to obtain a tracking-locked state in a short time. (Hereinafter this condition will be called a back lock state.) To solve this problem, it has been practiced to quickly obtain a tracking-locked state by shifting the track under control (controlling track) to the extent of two tracks. For this purpose, the VTR is preferably arranged to be capable of shifting the controlling track upon detection of the above stated back lock state as well as effecting change-over from one reproduction mode to another as necessary upon detection of the track pitch. However, for performing both of these actions, the conventional VTR is arranged to perform the two different detecting actions separately from each other. Therefore, the conventional arrangement has necessitated use of two different detecting circuits and thus resulted in a complex circuit arrangement.